MARTINEZ — In a ruling Monday, a Contra Costa County judge denied a new trial motion for a man who was convicted of murdering his ex-girlfriend in 1983.

Sherill Smothers, 56, of Granite Bay, now faces a likely 25 years to life prison sentence for the murder of Marsha Carter. In September, a jury convicted Smothers of first-degree murder. The case went unsolved for decades, until Smothers was linked to the crime through DNA evidence.

In the days after the trial, Smothers’ attorney raised concerns over evidence that he said implicated a Florida man in the crime. But Judge John Kennedy said he didn’t believe the new information was likely to change the jury’s mind.

In December 1983, Carter was murdered inside her Richmond home, brutally stabbed to death as her sons slept. Her body was placed inside the trunk of her car and moved to a Sacramento-area parking lot, where it was discovered days later.

Police found DNA not belonging to Carter or her family in two key places — blood in her bathroom that was linked in 2016 to Smothers — and human DNA under her fingernails that was linked to a Florida man by a ratio of one in 2.4 million. When police tracked down the Florida man, he voluntarily provided DNA and said he was in the military and in Texas in 1983.

But during trial, prosecutors discovered that in 1983 the man was in the reserves — not at a military base as originally thought — and living in Wisconsin. When Smothers’ defense team looked into it, they found evidence to suggest the man traveled to California in 1983.

The man’s ex-wife testified at a hearing last week that in December 1983, he and others left on a road trip. She said she wasn’t sure where they went but that he came back with an Oakland Raiders jacket.

Smothers’ attorney, Michael Markowitz, said the gifted Raiders jacket was a strong indication the man had visited the Bay Area the month Carter was murdered. But Kennedy pointed out Monday that the Raiders were in Los Angeles from 1982 to 1994, though he said the team’s memorabilia was still likely available in the Bay Area.

“Oakland never lost its love for the Raiders, and they were constantly trying to get them back,” he said.

Prosecutor Chris Walpole had argued that the testimony about the Raiders jacket was the only piece of new information that had come in. He pointed out Markowitz had known about the fingernail DNA evidence during trial and had told the jury about it.

He said the jury’s verdict — which found Smothers not guilty of an enhancement charge of using a knife to commit the crime — indicated jurors believed Smothers planned the crime but may not have personally killed Carter.

Authorities believe Smothers had an accomplice, but the Florida man was never charged in Carter’s killing, and there is no known connection between him and Smothers. He has never been charged with being involved in the plot to murder her, which prosecutors say Smothers concocted our of anger when Carter ended their relationship.

Smothers, who is paralyzed and requires a wheelchair, was not present at Monday’s hearing. His attorney said Smothers has suffered an infection since being placed in a hospital while awaiting transfer to a California prison. Smothers was badly injured in a car crash in the late 1980s and was awarded a $6.1 million judgment in a lawsuit that followed.